Diesel hydrofining—hydrogenation pour point depression technology
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Today I read an article about diesel fluidity reduction; the process involved is essentially based on modifications to hydrogenation units, with the key changes lying in the reactor section. It involves the use of hydrogenation-refining + hydrogen-assisted fluidity reduction technology, meaning two reactors are connected in series, with diesel first being refined and then having its fluidity reduced； Another option is to use just one reactor, with a refined catalyst in the upper section and a dew point depression catalyst in the lower section. The first method is understandable to everyone; I would like to learn more about the second technique, namely the one that uses only one reactor. During normal operation: 1. What percentage of the original hydrogenation refining capacity is processed? 2. How does the average temperature of the reactor change? 3. How does the temperature at the highest point of the catalyst bed change? 4. How does the pressure difference across the catalyst bed change? 5. How does the operating pressure of the reactor change? 6. How does the temperature at the reactor inlet change? I hope experienced colleagues will join the discussion and help resolve these issues!
If we use just one reactor as you said, how large would that reactor have to be? The processing capacity of a reactor also has to be low, because prior to using the pour-point depressant catalyst, pre-refining is necessary; and after using that catalyst, refining is required again. The inlet temperature for diesel fluidization depends on the pour-point depressant catalyst used as well as on the desired pour point – it’s difficult to give a specific value. The pressure, too, is determined by the catalyst. Pour-point depression is a process involving a temperature drop, usually of around 5 degrees at most; the specifics depend on the operating conditions.
Can it improve the color and quality of diesel?
This post was last edited by kaminocmyhc on 2011-2-10 at 16:08. Our diesel hydrotreating dewaxing unit uses precursors and post-treatments at the front and back, with a dewaxing agent placed in the middle. It has been running for 5 years now, and the performance is very good. However, I must mention that there is a small refining reactor in front of the anticoagulation reactor. The current processing capacity is 200,000 tons per year. As for the question raised by the original poster, it is related to the raw materials, the catalyst, and the duration of catalyst use. To put it simply, our current operating parameters are as follows: the inlet temperature for the refining reaction is around 336 degrees, with a pressure of about 4.35 MPa; the inlet temperature in the condensation section is around 387 degrees. After cooling, the pressure of the reaction products in the high-pressure tank is maintained at 3.8 MPa.
Could the original poster explain the principle of hydrodesaturation? Is it about isomerizing the diesel components of alkanes to lower their freezing point?
Principle of hydrodesensitization reaction. Hydrodesensitization is a typical shape-selective catalytic cracking reaction, and its reaction mechanism is similar to that of catalytic cracking; that is, the cracking reaction also takes place at proton acid sites, following the normal carbocation reaction mechanism； The difference is that the hydrogenation dew point depression catalyst is based on ZSM-5 zeolite, which consists of two interconnecting pore systems: linear pores and zigzag pores. The linear pore opening is an ellipse with dimensions of 0.53 nm × 0.56 nm; due to the constraints imposed by the zeolite’s special pores, only paraffins with a molecular diameter of less than 0.55 nm, alkanes with short side chains, and cycloalkanes with long side chains – namely those components with high freezing points – can be selectively cracked into smaller molecules, thereby reducing the freezing point of the oil. The remaining large-molecule isoparaffins, cycloalkanes, and aromatics cannot enter these pores and therefore do not undergo any reaction. Only long and narrow paraffin molecules in the diesel fraction can enter the micropores of the zeolite for cracking; therefore, the hydrodesulfurization process is also known as catalytic dewaxing process.
Application scope of demulsification technology: Single-stage hydrogenation demulsification is suitable for straight-run diesel with good raw material quality and high wax content, whereas hydrogenation demulsification is appropriate for processing catalytically treated diesel, coker diesel, and other secondary processed oils of lower quality, in order to produce high-quality low-viscosity diesel suitable as a clean fuel.
Dephasing is a hydrocracking reaction in which the heat released exceeds the heat absorbed; overall, it is still an exothermic reaction, so it is necessary to control the temperature rise in the bed. Whether the two units are connected in series or one unit is used in a through-flow configuration, a certain amount of refined catalyst must be installed below the dew point catalyst to saturate the unsaturated hydrocarbons produced by cracking.
Learn*la: What’s the difference between hydrogenation in the presence of hydrogen and hydrogenation itself? Could you explain it in more detail?
I also want to understand the differences between hydrogenation and hydrotreating. I heard there is also a non-hydrogen catalytic dewaxing technology. Does anyone know?